USABO Open Exam Questions with
Complete Solutions (Latest 2025)
Sunflower chromosomes have been isolated and their
DNA/NT analyzed. It was found that chromosome 2 has
unusually high content of Adenine (40%). How many percent
of Guanine is present in chromosome 2?
A. 10%
B. 20%
C. 30%
D. 40 %
E. 50% - Correct Answers ✅A. 10%
Sunflower chromosomes have been isolated and their
DNA/NT analyzed. It was found that chromosome 2 has
unusually high content of Adenine (40%). Assume that the
entire sequence of the chromosome is transcribed. Which of
the following is true for the content of Adenine in the
transcribed RNA?
A. Adenine is 40% of the RNA.
B. Adenine is 20% of the RNA.
C. Adenine is at least 20% of the RNA.
D. Adenine is at least 40% of the RNA.
E. The content of Adenine is not possible to determine based
on the information provided. - Correct Answers ✅E. The
content of Adenine is not possible to determine based on the
information provided.
,USABO Open Exam Questions with
Complete Solutions (Latest 2025)
Which of the following is a primary organ or structure of the
immune system?
A. Spleen
B. Thymus
C. Tonsils
D. Lymph nodes
E. Appendix - Correct Answers ✅B. Thymus
"Hairs" (such as trichomes) on the surface of leaves may
limit:
A. photosynthesis.
B. intake of carbon dioxide.
C. evapotranspiration.
D. drought adaptations.
E. movement of water in the vessels. - Correct Answers
✅C. evapotranspiration.
You discover a worm-like organism that inhabits soil samples
that has the following characteristics: segmented body and
few bristle-like extensions. To which one of the following
groups will you assign this organism?
, USABO Open Exam Questions with
Complete Solutions (Latest 2025)
A. Cestoda
B. Polychaeta
C. Oligochatea
D. Onychophora
E. Myriapoda - Correct Answers ✅C. Oligochatea
Evolution is a product of:
A. realized niche and biomagnification.
B. phenotypic variation and selective pressures.
C. rainfall and temperature.
D. adaptability within one generation.
E. extinction and landscape variability. - Correct Answers
✅B. phenotypic variation and selective pressures.
Which of the following is NOT true of allosterically regulated
enzymes?
A. Their activity can be modulated by effector molecules.
B. They demonstrate cooperativity.
C. Their activity can be modulated by substrate
concentration.
Complete Solutions (Latest 2025)
Sunflower chromosomes have been isolated and their
DNA/NT analyzed. It was found that chromosome 2 has
unusually high content of Adenine (40%). How many percent
of Guanine is present in chromosome 2?
A. 10%
B. 20%
C. 30%
D. 40 %
E. 50% - Correct Answers ✅A. 10%
Sunflower chromosomes have been isolated and their
DNA/NT analyzed. It was found that chromosome 2 has
unusually high content of Adenine (40%). Assume that the
entire sequence of the chromosome is transcribed. Which of
the following is true for the content of Adenine in the
transcribed RNA?
A. Adenine is 40% of the RNA.
B. Adenine is 20% of the RNA.
C. Adenine is at least 20% of the RNA.
D. Adenine is at least 40% of the RNA.
E. The content of Adenine is not possible to determine based
on the information provided. - Correct Answers ✅E. The
content of Adenine is not possible to determine based on the
information provided.
,USABO Open Exam Questions with
Complete Solutions (Latest 2025)
Which of the following is a primary organ or structure of the
immune system?
A. Spleen
B. Thymus
C. Tonsils
D. Lymph nodes
E. Appendix - Correct Answers ✅B. Thymus
"Hairs" (such as trichomes) on the surface of leaves may
limit:
A. photosynthesis.
B. intake of carbon dioxide.
C. evapotranspiration.
D. drought adaptations.
E. movement of water in the vessels. - Correct Answers
✅C. evapotranspiration.
You discover a worm-like organism that inhabits soil samples
that has the following characteristics: segmented body and
few bristle-like extensions. To which one of the following
groups will you assign this organism?
, USABO Open Exam Questions with
Complete Solutions (Latest 2025)
A. Cestoda
B. Polychaeta
C. Oligochatea
D. Onychophora
E. Myriapoda - Correct Answers ✅C. Oligochatea
Evolution is a product of:
A. realized niche and biomagnification.
B. phenotypic variation and selective pressures.
C. rainfall and temperature.
D. adaptability within one generation.
E. extinction and landscape variability. - Correct Answers
✅B. phenotypic variation and selective pressures.
Which of the following is NOT true of allosterically regulated
enzymes?
A. Their activity can be modulated by effector molecules.
B. They demonstrate cooperativity.
C. Their activity can be modulated by substrate
concentration.
